Everyone here is super quick to defend or bash the post without actually thinking about it. There are plenty of champions in league right now that you could go 0/6, get their core built, then kill the opposing 6/0 laner with little to no trouble, playing the exact same way they were playing before they got the items.
Individual circumstances of this, yes, you can argue all sorts of different points like "he could just be better", "they played better as a team", etc. but when it all boils down, league's tier lists are VERY rigid because of the issue the OP is bringing forward. Each patch has a VERY rigid S tier list because those champions can only be handled by other S tier champions, and sometimes simply can't be handled no matter how shit the player is once they get their core items.
This isn't an issue that is widespread over every game you're gonna play, but as several other people have said, banning/counterpicking is not a valid point of balance. Sure, Riot manages to (usually over 3-4 patches) FINALLY stop some champs from being near 100% pick/ban, but that doesn't matter when the next patch brings out a new set of pick/ban balance issues.
Riot needs to spend more time on each individual patch instead of releasing broken mechanic after broken mechanic, fixing a few along the way here and there.
League has stood the test of time because it is ever-changing, evolving, adding new things to master and I love the game overall, but the balance team is ALL over the place. Sometimes they balance for solo queue, sometimes they ignore solo queue balance for several patches to get pro play in line, EVERY time they rush through a patch to try to release a new skin and make money and that sucks. Other games reach a state where they can't add anything without breaking the game, respect that barrier, and let the game be until the community dies. Riot just laughs while it breaks the game again and again to turn a profit.
I get it, Riot is a company that needs to make a profit, quit complaining, yada yada yada, but they shit on the integrity of the game to make money and that's the issue so many people have. They could just release new skins every few weeks to keep profits up while taking more time to clean up every single patch. That would provide more jobs for designers of skins, make a lot of players happy since they'd be able to do more skins for less than popular champions, and the balance team could actually make some solid work towards a balanced league of legends, but that isn't gonna happen.